Alterations in eicosanoid production play a complex role in cancers, including lung cancer. Preclinical studies from our group have demonstrated that increased levels of prostacyclin (PGI2) are chemopreventive in multiple models of lung cancer. Furthermore, the orally active PG12 analog iloprost has both chemopreventive and chemotherapeutic activity in mouse models of lung cancer. These studies resulted in a double-blind, placebo controlled clinical chemoprevention trial in which patients at high risk for lung cancer were treated with iloprost. This trial demonstrated significant reversal of endobronchial dysplasia in ex-smokers, one of the few chemopreventive trials to show a positive effect. There are cun-ently plans to move forward PGI2 analogs in a larger Phase ll/Phase III trial examining the prevention of lung cancer. We demonstrated that the protective effects of PGI2 were independent of the cell surface receptor, but were mediated through activation of the nuclear receptor PPARy. These studies, along with retrospective studies showing reduced incidence of lung cancer in patients taking thiazolidinediones (TZDs), resulted in a second, ongoing clinical trial assessing the role of the TZD pioglitazone in patients at risk for lung cancer (PIOuS trial). The goal of the current proposal is to examine PGI2 analogs and define the cellular and molecular mechanisms mediating the effects of PGI2 analogs and pioglitazone. Three specific aims are proposed. Due to the discontinuance of oral iloprost. Aim 1 will test the preventive and therapeutic effects of two novel PGI2 analogs, treprostinil and inhaled iloprost. Aim 2 will define the cellular and molecular targets of PGI2 and PPARy. Alterations in inflammatory cells will be examined in mouse models and biopsies from clinical trials to determine if changes in these cell populations are associated with response. In murine models, targeted deletions of PPARy in myeloid cells and epithelial cells will be used to define the critical target cell mediating the chemopreventive response of PGI2 and PPARy. Our studies have demonstrated that expression of the Wnt receptor Frizzled 9 (Fzd9) is necessary for growrth inhibition and activation of PPARy in human NSCLC. The role of Fzd9 in mediating the chemopreventive effects of PGI2 will be determined using Fzd9 knockout mice. Finally, Aim 3 will examine samples from both the completed iloprost trial and the PIOuS trial to develop both prognostic biomarkers that characterize dysplasia risk and predictive biomari<ers for response to lloprost and PPARy modifying therapies. We expect that completion of these aims will provide a fundamental understanding of the mechanisms regulated by these agents, and lead to novel targets for chemoprevention. as well as define criteria for patient selection in future Phase ll/lll trials using these agents to prevent lung cancer. REtEVANCE (See instructions): Based on preclinical studies performed in this project, prostacyclin analogs and activators of PPARy have shown great promise as chemopreventive agents in patients at risk for lung cancer. The goal of this project is to determine the mechanisms of action of these agents, and to define biomarkers in biopsies from patients in order to develop a better strategy for targeted personalized chemoprevention of lung cancer.